Separation of oil and water from oily water is a common task in many hydrocarbon processing facilities, and there are numerous manners of such separation known in the art. For example, U.S. Pat. No. 4,088,578 describes a system in which oil and water are separated using a settling scheme based on the specific gravities of the water and oil. Alternatively, as exemplarily described in U.S. Pat. No. 4,359,386, a plurality of filters is used for separation of oil from water. In still further known methods, a cyclone-stripper combination may be employed as shown in U.S. Pat. No. 5,368,700. Distillation, typically at reduced pressure, has been disclosed is U.S. Pat. No. 5,980,694. Similarly, U.S. Pat. No. 4,089,662 teaches a vaporizer that is coupled to a column to separate the water phase from oily water produced in the column. In yet further known methods, U.S. Pat. No. 5,100,546 teaches use of a chemical absorbent, while U.S. Pat. No. 5,188,742 discloses a process in which the oil that is separated from the oily water is combusted.
While most of such systems are at least somewhat effective for their intended purpose, most if not all of those methods have significant disadvantages when employed in the on-line separation of water from oily water produced in a column. It should be noted that water that is dissolved and entrained in refinery and natural gas plant feed gases often creates fractionation difficulties, especially in deethanizer columns where water tends to become trapped and cause excessive internal reflux and product losses. Moreover, oily water from a column is typically not suitable for discharge into a sewer or the environment as such water is contaminated with sulfurous compounds (e.g., mercaptans and H2S), heavy hydrocarbons (e.g., benzene and toluene), and/or other undesirable components.
To circumvent difficulties associated with excess water in separation columns, the column bottom temperature is typically increased to drive the water content overhead. While such method is conceptually relatively simple and often removes significant quantities of water from the column, significant operational disadvantages remain. For example, higher reboiler duties are generally required for such operation, which increases flooding and steam demand. Moreover, higher bottoms temperatures also often result in product losses. For instance, increasing bottom temperature from 220° F. to 240° F. in a deethanizer column typically accounts for 10% to 20% propane losses. Other known methods of water removal have proved to be equally ineffective and costly. For example, a chimney tray can be incorporated with sufficient residence time for water oil separation. However, a calming zone that is required for phase separation rarely exists inside the fractionation column (e.g., due to the turbulent environment), rendering such alternatives often ineffective, if not impossible.
Therefore, while various oil water separation devices and methods are known in the art, all or almost all of them suffer from one or more disadvantages, especially where oily water separation is required for stable column operation. Consequently, there is still a need for improved configurations and methods of oil water separation, especially for separation columns.